The purpose of precooling is to reduce field heat. Retaining the freshness of grapes for a long time requires prompt removal of field heat after harvesting. The temperature in the packing house should be maintained at 18 to 20°C and the grapes should be transported to precooling units within 4–6 h of harvest.
We will look at step by step process for grapes precooling:
1. Grading: After harvesting of Grapes, it should be graded with different size, color and maturity. So, we can separate the good quality grapes for selling purpose.
2. Packing: We should pack the grapes after grading the grapes. The packing should be in correct size and perfect one.
3. Palletization: After packing, the packed fruits are kept in wooden/plastic pallets with proper ventilation. And then shifted to the pre-cooling room.
4. Pre-cooling: Pre-cooling is the process to decrease the grapes temperature quickly in the harvesting land. So, we can reduce the wastage of grapes. Pre cooling was done Within 4-6 hrs of harvest period. Forced air cooling method used for pre-cooling of grapes.
Forced air cooling was developed to accommodate products requiring relatively rapid removal of field heat immediately after harvest. Forced air or pressure cooling is a modification of room cooling and is accomplished by exposing packages of produce to higher air pressure on one side than on the other. This technique involves definite stacking patterns and the baffling of stacks so that the cooling air is forced through (rather than around) the individual containers. Differential pressures in use are approximately 0.6 to 7.5 mbar with air flows ranging from 0.001to 0.003 m3/s kg product./s kg product.
5. Cold storage: Recommended storage temperatures for table grapes are 0 to 2 °C. The relative humidity should be maintained around 95%. Although temperatures as low as -2°C have not been injurious to well-matured fruit of some varieties, other varieties of low sugar content have been reported damaged by exposure to - 1.7 °C. Generally 0°C can be considered the Optimum value for storage temperature. In the cold storage rooms uniform air circulation should be provided, but air velocity should be lower than 0.1 m/s in the channels between the pallets in order to minimize the loss of moisture from the stems. Large diameter fan, possibly with double speed,should be installed in order to adapt air movement to temperature level and quantity of product stored.
6. Transport: Finally the stored grapes transported to the distributor and then going to consumer.
